<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="./css/main.css">
    <style>
        .a {
            color: red;
        }

        .b {
            font-size: 2rem;
        }

        .c {
            border: solid;
        }
    </style>
</head>

<body>
    <div id="box" style="" class="a b c">hello jack</div>
    <script>
        const box = document.getElementById('box');

        console.log(box.style.color);
        setTimeout(() => {
            box.style.color = 'green';
            box.style.fontSize = '3rem';
            // -moz-border-radius
            // MozBorderRadius
        }, 2000);

        setTimeout(() => {
            box.style.color = '';
            box.style.fontSize = '';
        }, 4000);

    </script>
</body>

</html>